Oxidised metalliferous materials such as laterites can have a refractory characteristic. For this reason smelting processes have been used to recover metals such as nickel and cobalt from such materials. However, the severe environmental repercussions of smelting processes have lead to the development of hydrometallurgical recovery processes for some oxidised metalliferous materials.
Known hydrometallurgical processes for the recovery of metals such as nickel and/or cobalt from laterite ores have primarily involved pressure acid leaching, typically at high pressures and employing sulfuric acid. Sulfuric acid is employed because of its abundance, cost and well-known chemistry. U.S. Pat. No. 6,261,527 does discloses a hydrometallurgical process for the recovery of nickel and/or cobalt from laterite ores involving atmospheric pressures, however, it still employs sulfuric acid leaching.
Recently, a process has been proposed which is based on a chloride acid leach as opposed to a sulphuric acid leach. Whilst a chloride leaching medium is a powerful lixiviant, it is corrosive and requires apparatus to be chloride resistant. Chloride media have also been avoided because they have a high acid consumption and can present difficulties with the control of iron and magnesium leaching, both metals typically present in laterites.
The company Chesbar Resources (now known as Jaguar Nickel Inc.) presented a paper at the ALTA 2002 Conference (Nickel/Cobalt-9 session) in Perth, Western Australia on May 18-20, 2003. The paper entitled “Beyond PAL: The Chesbar Option, AAL” outlined a process for the atmospheric chloride acid leaching of nickel laterite ores. The process is now disclosed in WO 2004/101833.
The Chesbar process requires the use of a pyrohydrolysis stage to regenerate from the process liquor HCl as a gas for recycle to leaching, and to regenerate magnesium oxide for use in a nickel/cobalt precipitation stage. However, HCl gas is difficult to handle, being highly corrosive. In addition, a pyrohydrolysis stage is endothermic, requiring the input of significant energy, and hence has both high capital and operating costs.
It would be advantageous if a halide based process could be provided for the recovery from oxidised metalliferous materials of metals such as nickel, cobalt, copper, precious metals, magnesium etc, which does not require a pyrohydrolysis stage and which does not require recycle of a corrosive gas for the acid leaching stage.